Hash is used to verify that data was not tempered during transmission. Hash is a checksum value generated and assigned to a file. Hash generation is only happen once; we cannot get a value out of hash. In some instances, we don’t even store a password but its hash value. We authenticate password by simply converting it into hash value and than comparing hash value and stored hash value in the database. If both match we’ll authenticate.

.NET Framework includes keyed and non-keyed algorithms and each is derived from System.Security.Cryptography.HashAlgorithm class which is based on System.Security.Cryptography.

Non-keyed Algorithms

 

Abstract Class	Description
MD5	Message Digest algorithm
RIPEMD160	MD160 hash algorithm
SHA1	Hash Algorithm 1
SHA256	Hash Algorithm 256
SHA384	Hash Algorithm 384
SHA512	Hash Algorithm 512

Keyed Algorithms

 

Class	Description
HMACSHA1	Hash-based Message Authentication Code using SHA1
MACTripleDES	Message Authentication Code using TripleDES

Computing non-keyed hash is simple

MD5 myHash = new MD5CryptoServiceProvider();

FileStream file = new FileStream(args[0], FileMode.Open, FileAccess.Read);
BinaryReader reader = new BinaryReader(file);

myHash.ComputeHash(reader.ReadBytes((int)file.Length));

Console.WriteLine(Convert.ToBase64String(myHash.Hash));

And keyed hash

byte[] saltValueBytes = Encoding.ASCII.GetBytes("This is my sa1t");
Rfc2898DeriveBytes passwordKey = new Rfc2898DeriveBytes(args[0], saltValueBytes);
byte[] secretKey = passwordKey.GetBytes(16);

HMACSHA1 myHash = new HMACSHA1(secretKey);

FileStream file = new FileStream(args[1], FileMode.Open, FileAccess.Read);
BinaryReader reader = new BinaryReader(file);

myHash.ComputeHash(reader.ReadBytes((int)file.Length));

Console.WriteLine(Convert.ToBase64String(myHash.Hash));